I have what should be a schematic file from a vendor, its suffix is .sch. I tried opening it with Eagle CAD but it wouldn't open. I then looked at the file with a text editor and there seem to be some references to Orcad.

Does anyone know if .sch files are Orcad files, and if so where to get a free viewer program from?

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2

".sch" is the normal Eagle suffix for schematic file names, but also for other programs. Keep in mind that the Eagle file formats are completely different from version 5 to version 6. Version 5 are binary and version 6 XML based. If Eagle 5 failed to open the file, it could still be a Eagle 6 file.
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Olin LathropMar 13 '12 at 17:42

1

SCH is often used, I believe Protel(Altium) used it, Eagle, and some other open source editors as well. I am afraid it's hard to tell what it is, other than trying all the schematic tools out there (or understanding your source better!)
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HansMar 13 '12 at 17:56

@OlinLathrop That sounds horrible! I would have imagined that they would have changed the suffix when they changed the format of the file.
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KellenjbMar 13 '12 at 18:14

I would try opening with a text editor first to see if possibly the data is human readable and they signed it. More reasonably, as the person whom gave you the schematic!
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Kortuk♦Mar 13 '12 at 18:17

4 Answers
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Orcad, PADS and Protel all used .sch at one point and there is no standard implied with the file type. Orcad now uses .DSN. Check with the vendor. Most commercial products offer a free reader (aka viewer) or a free Lite version that limits modification but not the open, so users can view files.